In the field of data transmission by which digital data representing various kinds of signal information are transmitted, there have been proposed to subject digital data which are to be transmitted to enciphering process at a transmission side and to reproduce original data by subjecting the enciphered digital data to deciphering process at a receiving side, in order to prevent the digital data from being eavesdropped on a data transmission line. Typical algorisms for enciphering digital data are the DES (Date Encryption Standard) published in 1977 by the National Bureau of Standards, the United State of America, and the RSA (Rivest, Shamir, Adleman) published in 1978 by the Massachusetts Institute of Technology.
With cipher-transmission based on the DES, digital data are enciphered in accordance with the rules determined by enciphering key data prepared previously to produce enciphered digital data and the enciphered digital data are deciphered in accordance with the rules determined by deciphering key data prepared previously to reproduce original digital data. The deciphering key data are prepared to be the same as the enciphering key data so that each of the deciphering key data and the enciphering key data are formed with common data (common key data). Although the algorisms for enciphering and deciphering have been opened to the public, the common key data are kept in secret for the purpose of enciphering.
With cipher-transmission based on the RSA, digital data are enciphered in accordance with the rules determined by enciphering key data to produce enciphered digital data and the enciphered digital data are deciphered in accordance with the rules determined by deciphering key data which has contents different from those of the opened enciphering key data to reproduce original digital data. Although the enciphering key data are not kept in secret to be open key data, the deciphering key data are kept in secret to be secret key data for the purpose of enciphering.
FIG. 1 shows a basic structure of a cipher-transmission system according to the DES. In the basic structure shown in FIG. 1, digital data to be transmitted are supplied to a DES enciphering portion 11 as original data. Common key data prepared previously are also supplied to the DES enciphering portion 11. In the DES enciphering portion 11, the original data are subjected to the DES enciphering process in accordance with the rules determined by the common key data to produce enciphered data. The enciphered data obtained from the DES enciphering portion 11 are transmitted through a data transmission line 12 having one end thereof connected with the DES enciphering portion 11.
The enciphered data having been transmitted through the data transmission line 12 are supplied to a DES deciphering portion 13 with which the other end of the data transmission line 12 is connected. The common key data which is the same as the common key data supplied to the DES enciphering portion 11 are also supplied to the DES deciphering portion 13. In the DES deciphering portion 13, the enciphered data are subjected to the DES deciphering process in accordance with the rules determined by the common key data to reproduce the original data.
FIG. 2 shows a basic structure of a cipher-transmission system according to the RSA. In the basic structure shown in FIG. 2, digital data to be transmitted are supplied to an RSA enciphering portion 14 as original data. Open key data prepared previously are also supplied to the RSA enciphering portion 14. In the RSA enciphering portion 14, the original data are subjected to the RSA enciphering process in accordance with the rules determined by the open key data to produce enciphered data. The enciphered data obtained from the RSA enciphering portion 14 are transmitted through a data transmission line 15 having one end thereof connected with the DES enciphering portion 11.
The enciphered data having been transmitted through the data transmission line 15 are supplied to an RSA deciphering portion 16 with which the other end of the data transmission line 15 is connected. Secret key data which have contents different from those of the open key data supplied to the RSA enciphering portion 14 are also supplied to the RSA deciphering portion 16. In the RSA deciphering portion 16, the enciphered data are subjected to the RSA deciphering process in accordance with the rules determined by the secret key data to reproduce the original data.
In the case of the DES enciphering and deciphering, the quantity of operations for enciphering data and deciphering enciphered data is relatively small and therefore high speed proceeding can be performed. On the other hand, in the case of the RSA enciphering and deciphering, the quantity of operations for enciphering data and deciphering enciphered data is relatively large and therefore high speed proceeding can not be expected.
In the field of video signals, digitalization of video signals has been aimed for actualizing diversification in information to be transmitted, improvements in quality of images reproduced from the video signal and so on. For example, there has been proposed the High Definition Television (HDTV) system which uses a digital video signal composed of digital word sequence data representing video signal information. The digital video signal under the HDTV system (hereinafter, referred to the HD signal) is formed in accordance with, for example, the BTA S-002 which is one of a series of standards established by the Broadcasting Technology Association (BTA) in Japan so as to be in the form of Y and PB/PR signals or G, B and R signals. In the case of the Y and PB/PR signals, Y represents a luminance signal and PB/PR represent color difference signals. In the case of the G, B and R signals, G, B and R represent green, blue and red primary color signals, respectively.
The HD signal is a digital television signal by which each frame picture is formed with first and second field pictures each appearing at a rate of 60 Hz and which is constituted in accordance with an arrangements including a frame rate of 30 Hz, 1125 lines per frame, 2,200 data samples per line and a sampling frequency of 74.25 MHz. For example, the HD signal in the form of Y and PB/PR signals is constituted in accordance with such data formats as shown in FIGS. 3A and 3B.
The data formats shown in FIGS. 3A and 3B include a part of a portion corresponding to a line period (hereinafter, referred to a line period portion) of a luminance signal data sequence (hereinafter, referred to a Y data sequence) as shown in FIG. 3A, which represents a luminance signal component of a video signal, and a part of a line period portion of a color difference signal data sequence (hereinafter, referred a PB/PR data sequence) as shown in FIG. 3B, which represents color difference signal components of the video signal. Each of data words constituting the Y data sequence or the PB/PR data sequence is composed of 10 bits. This means that each of the Y data sequence and the PB/PR data sequence constitutes 10-bit word sequence data having a word transmission rate of, for example, 74.25 Mwps.
In the Y data sequence shown in FIG. 3A, each line period portion of which is formed with a portion corresponding to a horizontal blanking period and a portion corresponding to a video data period appearing after the horizontal blanking period, time reference code data SAV (Start of Active Video) which are composed of four 10-bit words (3FF(Y), 000(Y), 000(Y), XYZ(Y): 3FF and 000 are hexadecimal numbers and (Y) indicates a word contained in the Y data sequence) are provided just before the portion corresponding to the video data period and another time reference code data EAV (End of Active Video) which are composed of four 10-bit words (3FF(Y), 000(Y), 000(Y), XYZ(Y)) are provided just after the portion corresponding to the video data period. Similarly, in the PB/PR data sequence shown in FIG. 3B, each line period portion of which is formed with a portion corresponding to a horizontal blanking period and a portion corresponding to a video data period appearing after the horizontal blanking period, time reference code data SAV which are composed of four 10-bit words (3FF(C), 000(C), 000(C), XYZ(C): (C) indicates a word contained in the PB/PR data sequence) are provided just before the portion corresponding to the video data period and another time reference code data EAV which are composed of four 10-bit words (3FF(C), 000(C), 000(C), XYZ(C)) are provided just after the portion corresponding to the video data period. The time reference code data EAV and SAV contained in the Y data sequence are provided in the portion corresponding to the horizontal blanking period of the Y data sequence and the time reference code data EAV and SAV contained in the PB/PR data sequence are provided in the portion corresponding to the horizontal blanking period of the PB/PR data sequence.
Initial three 10-bit words (3FF, 000, 000) of four 10-bit words (3FF, 000, 000, XYA), each of which is shown with (Y) or (C), are used for establishing word synchronization or line synchronization and a last one 10-bit word (XYZ) of four 10-bit words (3FF, 000, 000, XYA), which is also shown with (Y) or (C), is used for discriminating the first field from the second field in each frame or for discriminating the time reference code data EAV from the time reference code data SAV.
In the portion corresponding to the horizontal blanking period in each of the Y data sequence and the PB/PR data sequence, line number data LN0(Y) and LN1(Y) or LN0(C) and LN1(C) which represent the number of each of line period portions constituting a frame period portion, error detection code data YCR0 and YCR1 or CCR0 and CCR1, and ancillary data YA0, YA1, . . . , YA267 or CA0, CA1, . . . , CA267 including audio data are provided between the time reference code data EAV and the time reference code data SAV.
When the HD signal constituted with the Y data sequence and the PB/PR data sequence is subjected to transmission through a data transmission line, it is desired for the HD signal to be converted to serial data from word sequence data so as to be subjected to serial transmission through a simplified data transmission line. In connection with the serial transmission of the HD signal constituted with the Y data sequence and the PB/PR data sequence, it has been standardized to transmit the HD signal in conformity with the HD SDI (High Definition Serial Digital Interface) according to the BTA S-004 which is one of a series of standards established by the BTA in Japan.
In the transmission of the HD signal in conformity with the HD SDI, the Y data sequence and the PB/PR data sequence are multiplexed, with their portions corresponding to the horizontal blanking periods in each of which the time reference code data EAV and SAV are provided and which synchronize with each other, to produce a multiple word sequence data as shown in FIG. 4 and then the multiple word sequence data are converted into serial data to be transmitted. Each of data words constituting the multiple word sequence data shown in FIG. 4 is composed of 10 bits and the word transmission rate of the multiple word sequence shown in FIG. 4 is set to be 74.25 Mwps×2=148.5 Mwps. In the multiple word sequence data thus obtained as shown in FIG. 4, multiple time reference code data (multiple SAV) which are composed of eight 10-bit words (3FF(C), 3FF(Y), 000(C), 000(Y), 000(C), 000(Y), XYZ(C), XYZ(Y)) are provided just before the portion corresponding to a video data period and another multiple time reference code data EAV (multiple EAV) which are composed of eight 10-bit words (3FF(C), 3FF(Y), 000(C), 000(Y), 000(C), 000(Y), XYZ(C), XYZ(Y)) are provided just after the portion corresponding to the video data period.
The each of the 10-bit words constituting the multiple word sequence data is sent bit by bit from its least significant bit (LSB) to its most significant bit (MSB) so that the multiple word sequence data are converted into a serial data. Then, the serial data is subjected to scrambling process to produce a serial transmission HD signal (hereinafter, referred to an HD-SDI signal) and the HD-SDI signal is transmitted through a data transmission line. The HD-SDI signal thus transmitted has a bit transmission rate of, for example, 148.5 Mwps×10=1.485 Gbps.
In the case of the transmission of the HD-SDI signal through the data transmission line, it is also desired to subject the HD-SDI signal to enciphering process at a transmission side and to reproduce original HD-SDI signal by subjecting the enciphered HD-SDI signal to deciphering process at a receiving side, in order to prevent the HD-SDI signal from being eavesdropped on the data transmission line. It may be said that the DES enciphering and the EDS deciphering are suitable for the cipher-transmission of the HD-SDI signal because high speed proceeding is desired for enciphering the HD-SDI signal and deciphering the enciphered HD-SDI signal. When the DES enciphering and the EDS deciphering are applied for the cipher-transmission of the HD-SDI signal, a cipher-transmission system which is similar to the cipher-transmission system according to the DES having the basic structure shown in FIG. 1 can be theoretically used.
For example, when an HD signal is converted into an HD-SDI signal in accordance with the HD SDI to be transmitted through a data transmission line and the transmitted HD-SDI signal is reconverted into the HD signal in accordance with the HD SDI to be supplied to, for example, a video projector which operates to display images based on the HD signal, it is considered to have such a cipher-transmission system as shown in FIG. 5 for conducting the cipher-transmission of the HD-SDI signal.
In the cipher-transmission system shown in FIG. 5, an HD-SDI signal DHS sent from an HD-SDI signal generating portion 20, in which an HD signal obtained from a video camera or the like is converted into the HD-SDI signal DHS in accordance with the HD SDI, is supplied to a DES enciphering portion 21 for HD-SDI signal. Common key data DEY prepared previously are also supplied to the DES enciphering portion 21 for HD-SDI signal. In the DES enciphering portion 21 for HD-SDI signal, the HD-SDI signal DHS is first subjected to serial to parallel (S/P) conversion to reproduce the original HD signal constituted with Y and PB/PR data sequences and the reproduced HD signal is subjected to the DES enciphering process in accordance with the rules determined by the common key data DEY to produce an enciphered HD signal. Then, in the DES enciphering portion 21 for HD-SDI signal, the enciphered HD signal is subjected to parallel to serial (P/S) conversion to produce an enciphered HD-SDI signal DHSE.
When the enciphered HD signal is produced by subjecting the HD signal to the DES enciphering process, for example, video data DVV which are provided in a portion corresponding to a video data period and time reference code date EAV which are provided in a starting end of a portion corresponding to a horizontal blanking period successive to the portion corresponding to the video data period in a portion corresponding to a line period of an HD signal constituted with Y and PB/PR data sequences shown in FIGS. 3A and 3B, as shown in FIG. 6, are subjected to the DES enciphering process to produce an enciphered video data. On the other hand, various data provided in the portion corresponding to the horizontal blanking period except the time reference code date EAV, that is, line number data DLN representing a line number varying line by line, error detection code data CRCC, ancillary data DAA including audio data, and time reference code data SAV, are not subjected to the DES enciphering process but combined with the enciphered video data. As a result, the enciphered HD signal which contains the various data provided in the portion corresponding to the horizontal blanking period except the time reference code date EAV and the enciphered video data successive to the portion corresponding to the horizontal blanking period is obtained.
The enciphered HD-SDI signal DHSE is sent from the DES enciphering portion 21 for HD-SDI signal to be transmitted through a data transmission line 22 having one end thereof connected with the DES enciphering portion 21 for HD-SDI signal.
The enciphered HD-SDI signal DHSE having been transmitted through the data transmission line 22 is supplied to a DES deciphering portion 23 for HD-SDI signal, with which the other end of the data transmission line 22 is connected. The common key data DEY which is the same as those supplied to the DES enciphering portion 21 are also supplied to the DES deciphering portion 23. In the DES deciphering portion 23, the enciphered HD-SDI signal DHSE is subjected to the S/P conversion to reproduce the enciphered HD signal constituted with the enciphered Y and PB/PR data sequences each containing the enciphered video data and the enciphered HD signal is subjected to the DES deciphering process in accordance with the rules determine ed by the common key data DEY to reproduce the original HD signal constituted with the Y and PB/PR data sequences.
When the HD signal constituted with the Y and PB/PR data sequences is reproduced by subjecting the enciphered HD signal to the DES deciphering process, the enciphered video data in the portion corresponding to the horizontal blanking period of the enciphered HD signal are subjected to the DES deciphering process to reproduce the original video data and time reference code data EAV. On the other hand, the various data provided in the portion corresponding to the horizontal blanking period except the time reference code date EAV, that is, the line number data DLN representing the line number varying line by line, the error detection code data CRCC, the ancillary data DAA including the audio data, and the time reference code data SAV, are not subjected to the DES deciphering process but extracted as they are to be combined with the reproduced video data and time reference code data EAV. As a result, the original HD signal as shown in FIG. 6 is obtained.
Then, in the DES deciphering portion 23 for HD-SDI signal, the Y and PB/PR data sequences constituting the reproduced HD signal are multiplexed with each other in accordance with the HD SDI to produce a word multiple data sequence and the word multiple data sequence thus obtained are subjected to the P/S conversion to reproduce the HD-SDI signal DHS.
The HD-SDI signal DHS obtained from the DES deciphering portion 23 for HD-SDI signal is supplied to a video projector 24. In the video projector 24, the HD signal is reproduced from the HD-SDI signal DHS and used for display of images.
In such a manner as described above, when the DES enciphering and the DES deciphering are applied for the cipher-transmission of the HD-SDI signal, it is required that the common key data DEY are supplied to both of the DES enciphering portion 21 for HD-SDI signal and the DES deciphering portion 23 for HD-SDI. Therefore, it is necessary to transmit the common key data DEY supplied to the DES enciphering portion 21 for HD-SDI signal through some means toward the DES deciphering portion 23 for HD-SDI to be supplied thereto.
Accordingly, it is considered to transmit the common key data DEY, together with the enciphered HD-SDI signal DHSE obtained from the DES enciphering portion 21 for HD-SDI, from the side of the DES enciphering portion 21 for HD-SDI to the side of DES deciphering portion 23 for HD-SDI through the data transmission line 22. FIG. 7 shows a cipher-transmission system for transmitting the common key data DEY, together with the enciphered HD-SDI signal DHSE obtained from the DES enciphering portion 21 for HD-SDI, from the side of the DES enciphering portion 21 for HD-SDI to the side of DES deciphering portion 23 for HD-SDI through the data transmission line 22.
In the cipher-transmission system shown in FIG. 7, a key data inserting portion 25 is provided at the output end of the DES enciphering portion 21 for HD-SDI signal in which the HD-SDI signal DHS sent from the HD-SDI signal generating portion 20 is subjected to the DES enciphering process in accordance with the rules determined by the common key data DEY to produce the enciphered HD-SDI signal DHSE, and a key data extracting portion 26 is provided at the input end of a DES deciphering portion 23 for HD-SDI signal. In the key data inserting portion 25 to which the enciphered HD-SDI signal DHSE obtained from the DES enciphering portion 21 for HD-SDI signal and the common key data DEY are supplied, the common key data DEY are inserted into the enciphered HD-SDI signal DHSE so that the enciphered HD-SDI signal DHSE and the common key data DEY are transmitted through the data transmission line 22 to the DES deciphering portion 23 for HD-SDI signal.
In the key data extracting portion 26, the common key data DEY are extracted from the enciphered HD-SDI signal DHSE and the common key data DEY. The enciphered HD-SDI signal DHSE having passed through the key data extracting portion 26 and the common key data DEY obtained from the key data extracting portion 26 are supplied to the DES deciphering portion 23 for HD-SDI signal. In the DES deciphering portion 23 for HD-SDI signal, the enciphered HD-SDI signal DHSE is subjected to the DES deciphering process in accordance with the rules determined by the common key data DEY to reproduce the HD-SDI signal DHS to be supplied to the video projector 24.
However, in the case wherein the common key data DEY are transmitted from the side of the DES enciphering portion 21 for HD-SDI to the side of DES deciphering portion 23 for HD-SDI through the data transmission line 22 as mentioned above, it is much feared that the common key data DEY are eavesdropped on the data transmission line 22 by a mala fide holder and the enciphered HD-SDI signal DHSE sent from the DES enciphering portion 21 for HD-SDI signal is undesirably deciphered with the eavesdropped common key data DEY. This problem brings about serious obstacle to the cipher-transmission of the HD-SDI signal for which the DES enciphering and the DES deciphering are applied.
Accordingly, it is an object of the present invention to provide a method of enciphering data which is applicable to cipher-transmission of digital information data such as an HD-SDI signal, in which the digital information data are subjected to enciphering process using common key data or data corresponding to the common key data to produce enciphered digital information data to be transmitted in an enciphering portion, the enciphered digital information data are subjected to deciphering process using the common key data or the data corresponding to the common key data to reproducing the original digital information data in a deciphering portion, and the common key data or the data corresponding to the common key data are transmitted from the side of the enciphering portion to the side of the deciphering portion, and by which such a fear that the common key data or the data corresponding to the common key data are eavesdropped on the transmission thereof and the enciphered digital information data are undesirably deciphered with the eavesdropped common key data can be effectively reduced.
Another object of the present invention is to provide an apparatus for enciphering data in which the method of enciphering data mentioned above is carried out.
A further object of the present invention is to provide a method of deciphering data which is applicable to cipher-transmission of digital information data such as an HD-SDI signal, in which the digital information data are subjected to enciphering process using common key data or data corresponding to the common key data to produce enciphered digital information data to be transmitted in an enciphering portion, the enciphered digital information data are subjected to deciphering process using the common key data or the data corresponding to the common key data to reproducing the digital information data in a deciphering portion, and the common key data or the data corresponding to the common key data are transmitted from the side of the enciphering portion to the side of the deciphering portion, and by which the original digital information data can be surely reproduced based on the enciphered digital information data.
A further object of the present invention is to provide an apparatus for deciphering data in which the method of deciphering data mentioned above is carried out.
A further object of the present invention is to provide a method of enciphering and deciphering data corresponding to a combination of the above-mentioned method of enciphering data with the above-mentioned method of deciphering data.
A still further object of the present invention is to provide an apparatus for enciphering and deciphering data in which the method of enciphering and deciphering data mentioned above is carried out.